Fixes #10809

Add a subsection to request-config.md explaining how to use the encode option with encodeURIComponent for backends that require strict percent-encoding of query values.

The default axios encoder decodes %3A, %24, %2C and %20 for readability, which is correct per RFC 3986 but can cause issues with stricter backends. This documents the existing paramsSerializer.encode escape hatch with a clear example.

Summary by cubic

Documents how to use paramsSerializer.encode with encodeURIComponent in axios to emit strict RFC 3986 percent-encoding for query params. Helps users integrate with backends that reject readable characters in query values.

Description

• Summary of changes: Added a “Strict RFC 3986 percent-encoding” subsection to request-config.md with per-request and instance examples using encodeURIComponent.
• Reasoning: The default encoder decodes %3A, %24, %2C, and %20 for readability; some backends require strictly percent-encoded values.
• Additional context: Docs-only; no runtime or API changes.

Docs

• Updated docs/pages/advanced/request-config.md. No other docs changes needed.

Testing

• No tests added or changed. Docs-only change; tests not needed.

Semantic version impact

• Patch: documentation update only, no behavior changes.

^{Written for commit 6f30bec. Summary will update on new commits. Review in cubic}